Received 10 January 2008; accepted 1st July 2008; published online 24 October 2008

Abstract -
Little is known about the genetic basis of residual feed intake (RFI) variation in fish, since this trait is highly sensitive to environmental influences, and feed intake of individuals is difficult to measure accurately. The purpose of this work was (i) to assess the genetic variability of RFI estimated by an X-ray technique and (ii) to develop predictive criteria for RFI. Two predictive criteria were tested: loss of body weight during feed deprivation and compensatory growth during re-feeding. Ten heterozygous rainbow trout clones were used. Individual intake and body weight were measured three times at threeweek intervals. Then, individual body weight was recorded after two cycles of a three-week feed deprivation followed by a three-week re-feeding. The ratio of the
genetic variance to the phenotypic variance was found high to moderate for growth, feed intake, and
RFI (
,
,
, respectively).
The index that integrates performances achieved during deprivation and re-feeding periods explained
59% of RFI variations. These results provide a basis for further studies on the origin
of RFI differences and show that indirect criteria are good candidates for future selective
breeding programs.